The vetebrate muscle nicotinic ACh receptor is very likely the architect of a family of related receptor molecules. The polypeptide subunits are probably encoded by a multigene family. Whereas electroplax ACh receptors or electric fish and embryonic or denervated muscle can be purified in sufficient quantity for detailed biochemical analysis, the putative nACh receptors in the central nervous system and the muscle synapse specific form occur in extremely small quantities and are very difficult to purify. Protein chemical methods cannot identify the relatedness of the non-abundant ACh receptor types or elucidate the molecular bases for the differences among ACh receptors. We propose to isolate by recombinant DNA techniques the cDNA's for each of the embryonic mouse muscle ACh receptor subunits. These cloned cDNA molecules will be used to characterize the nucleic acid and derive protein sequence; to characterize the expression of the ACh receptor mRNA's in different tissues; and to begin to analyze the organization of ACh receptor genes in the genome.